1. Technical Field
This disclosure generally relates to the field of luminaire, and more particularly to dissipation of the heat generated by ballast electronics of a luminaire.
2. Description of the Related Art
With increasing trend of energy conservation and for various other reasons, including replacement of gas-vapor lamps, solid-state lighting has become more and more popular as the source of illumination in a wide range of applications. As generally known, solid-state lighting refers to a type of lighting that emits light from a solid object, such as a block of semiconductor, rather than from a vacuum or gas tube as is the case in traditional lighting. Examples of solid-state lighting include light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), and polymer light-emitting diodes (PLEDs). Solid-state lighting as compared to traditional lighting generates visible light with reduced parasitic energy dissipation in the form of reduced heat generation. Further, solid-state lighting tends to have increased lifespan compared to traditional lighting. This is because, due to its solid-state nature, solid-state lighting provides for greater resistance to shock, vibration, and wear.
An LED lamp is a type of solid-state lighting that utilizes LEDs as a source of illumination, and typically has clusters of LEDs in a suitable housing. The LEDs in an LED lamp typically have very low dynamic resistance, with the same voltage drop for widely-varying currents. Thus, the LEDs cannot be connected directly to most power sources, such as the 120-volt AC mains commonly available in the U.S., without causing damages to the LEDs. Consequently, an electronic ballast is used to transform the high voltage and current from the AC mains into a typically lower voltage with a regulated current.
The electronic ballasts used in LED lamps have a typical conversion efficiency of 75%-95%, and more typically 85%. This means that 5% -25% of the energy used by a solid-state luminaire is wasted as heat, generated by the electronic ballast. This heat must be removed from the electronic ballast to prevent premature failure of the electronic components of the ballast. In a high-flux luminaire of, for example, 40 watts, about 8.8 watts of waste heat must be removed. However, passive cooling method using heat sink fins will not likely be able to keep temperature rise of the electronic components within safe limits if the ballast is installed in a recessed “can light” or security light type of luminaire. This is because, with such enclosed lamp mounting spaces, there is insufficient airflow to safely cool the electronic ballast.
There is, therefore, a need for an active cooling method and apparatus to more effectively remove the heat generated by the electronic ballast in a solid-state lighting, such as a LED lamp, to keep the temperature of the electronic components of the ballast within safe limits.